IMO abortion for any reason should be legal at any point in the pregnancy.
I don't say this lightly - I started off from a pro-life position. But that implies assumptions about women and babies that are very unpleasant.
If you can abort a baby with a condition (and it doesn't have to be life limiting or even severe - just a condition) up to term, then you should be able to abort any unborn infant up to term. Either abortion is OK, or it isn't. To say that it is OK when the baby is disabled is disablist and discriminatory.
To say that a potential person is less of a person because they don't "look" like a baby is weird IMO. A 21 week unborn child is just as much of a potential as a 6 week unborn child. They both have the same amount of humanity, you don't become more homo sapiens as you grow. The only value they have is that placed upon them by their environment. There is no external, objective measurement.
You cannot insist women carry and bear babies, whether disabled or not, because they have control and power over their bodies, which is a Good Thing. And you cannot ban abortion, because that leads to forced pregnancy, power over women, botched, hideous abortion and many other awful consequences.
Therefore, abortion has to be legal. Any limit that does not include all unborn babies is arbitary and discriminatory, since women cannot be forced to bear a disabled child, there should be no limit.
I don't actually like the opinion I have come to, but it is the only one that makes sense to me. I am pretty sure it puts me at odds with everyone though, please feel free to flame me for being over simplistic.
I do genuinely believe that removing the limit would not lead to a flurry of late term abortions - because it is not something anybody enters into lightly.